Fix unlikely but possible race in `WeakValueDictionary` It may happen that value in `valueArray` could have been already collected by the GC but #clearDeadSlots have not yet been called. When this happened, `#at:ifAbsentPut:` returned tombstone rather than updating the dictionary with value from block. This commit fixes this by checking whether `valueArray` contain the tombstone and if so, clearing up the dead slots and restarting the operation. HTH.

@REM -------
@REM make using Microsoft Visual C compiler
@REM type vcmake, and wait...
@REM do not edit - automatically generated from ProjectDefinition
@REM -------

@if not defined VSINSTALLDIR (
    pushd ..\rules
    call vcsetup.bat
    popd
)
@SET DEFINES=

make.exe -N -f bc.mak -DUSEVC=1 %DEFINES% %*